The present invention relates to a printer controller of color printer; more specifically, a printer controller that detects relative dislocation among colors in an electro-photographic tandem color image generator that uses a plurality of photosensitive elements. The detection of color dislocation is for the purpose of precise color alignment on a recording medium.
A data flow of in a conventional color image forming device is shown in FIG. 10.
An electro-photographic printer 31 generates an image based on print data delivered from a personal computer 30 (or a CAD, a work station, a digital camera or the like) to the printer 31 via an interface.
The printer 31 is formed of a printer controller and a color image generator (sometimes referred to as xe2x80x9cprinter enginexe2x80x9d, depending on situation).
The printer controller receives print data of a document to be printed delivered in the form of a mixture of print language and bit map data, or the like, and converts the data into raster data to enable a printer engine form an image. The printer engine forms a latent image in accordance with the raster data delivered form the printer controller. An image is thus created.
An image forming process in the electro-photography is described more in detail. A photosensitive drum, or an image carrier, is charged by a charger, and then irradiated with light in accordance with image information. A latent image thus formed is developed by a developer to become a toner image, which image is transferred on paper, or such other material that is an object of the transfer (hereinafter referred to as xe2x80x9ctransfer materialxe2x80x9d).
A tandem color image former as illustrated in FIG. 11 is proposed to better meet the needs of color image era.
As shown in FIG. 11, the color image generator comprises four image generating devices (hereinafter referred to as xe2x80x9cimaging stationxe2x80x9d) 1a, 1b, 1c, 1d, each of the imaging stations 1a, 1b, 1c, 1d is provided with a photosensitive drum (photosensitive element) 2a, 2b, 2c, 2d, respectively. Disposed around the drum includes a charger 3a, 3b, 3c, 3d, a developer 4a, 4b, 4c, 4d, a cleaner 5a, 5b, 5d, 5d, an exposure device having scanning optical system 6a, 6b, 6c, 6d, and a transfer device 8a, 8b, 8c, 8d for transferring toner image on a transfer belt 12, which being a part of transfer means 7.
At imaging stations 1a, 1b, 1c, 1d, an image is formed in yellow, in magenta, in cyan and in black, respectively. Exposure devices 6a, 6b, 6c, 6d irradiate exposure lights 9a, 9b, 9c, 9d, respectively, corresponding to the yellow image, magenta image, cyan image and black image.
Underneath the photosensitive drum 2a, 2b, 2c, 2d, an endless transfer belt 12 is provided, supported by rollers 10 and 1. The belt circulates in a direction as indicated with an arrow A.
A pattern detection device 14 is provided facing the transfer belt 12 for detecting a location detection pattern generated by location detection pattern generating means 13.
Transfer materials 17 stored in a paper dispenser cassette 16 are delivered via a paper feeding roller 18 to a transfer roller 19, a fixer 20, eventually to a paper tray (not shown).
In a color image generator of the above configuration, a black latent image is formed at the imaging station 1d on the photosensitive drum 2d by a known electro-photographic process. The latent image is developed at the developer 4d with a developer material containing black toner into visible black toner image. The black toner image is transferred at the transfer device 8d on the transfer belt 12.
While the black toner image is being transferred on the transfer belt 12, a cyan latent image is formed at the imaging station 1c. The latent image is developed at the developer 4c with a cyan toner into visible cyan toner image. The cyan toner image is transferred at the transfer device 8c to be overlaid on the black toner image.
Magenta toner image and yellow toner image formed through the same procedure are likewise transferred on the transfer belt 12. When the toner images of four colors are overlaid into a single image on the transfer belt 12, the complete toner image of four colors is transferred by the transfer roller 19 on paper or other such transfer material 17 delivered via feeding roller 18 from the paper dispenser cassette 16. The transferred image is fixed by heating at the fixer 20 as a full-color image on the transfer material 17.
After finishing the image transfer, the residual toner staying on the photosensitive drum 2a, 2b, 2c, 2d is removed by a cleaner 5a, 5b, 5c, 5d, and the photosensitive drum is ready for the next image formation.
The tandem color image generator of the above described configuration is advantageous in that it can provide color images at a high speed, since the image generator has independent imaging stations 1a-1d, each capable of forming a color image.
The above described tandem color image former, however, has a problem in how to precisely overlay respective images formed at independent imaging stations 1a-1d (viz. registration). The relative dislocation existing among the four color images transferred on the transfer material 17 eventually reveals itself as the dislocation or the color change in a finished picture.
There are five kinds of dislocations in the transferred image. FIG. 12(a) illustrates a dislocation in the direction of transfer (the direction indicated with arrow symbol A) of transfer material (hereinafter referred to as xe2x80x9csub scanning dislocationxe2x80x9d); FIG. 12(b) illustrates a dislocation in the direction of scanning (direction perpendicular to the arrow symbol A) (hereinafter referred to as xe2x80x9cmain scanning dislocationxe2x80x9d); FIG. 12(c) illustrates a dislocation in an oblique direction (hereinafter referred to as xe2x80x9cskew errorxe2x80x9d); FIG. 12(d) illustrates a dislocation caused by an error in the magnification factor; and FIG. 12(e) illustrates a dislocation due to curve error. In practical cases the dislocation appears as an integration of these causes.
The sub scanning dislocation shown in FIG. 12(a) stems mainly from dislocated installations of imaging stations 1a-1d, optical scanning systems, and dislocation of constituent lenses and mirrors (not shown) within the scanning optical system or such other reasons that come from mechanical causes. The main scanning dislocation shown in FIG. 12(b) also stems from the same reasons. The dislocation in an oblique direction shown in FIG. 12(c) is due to a dislocated angle of a revolving shaft of a photosensitive drum in the imaging stations 2a-2d, or dislocated installation of the optical scanning system. The dislocation due to error in the magnification factor shown in FIG. 12(d) stems from the variation in the length of scanning line caused as a result of an error in the length of light path from respective optical scanning system to the photosensitive drum 2a-2d at imaging station 1a-1d. The dislocation due to the curve error shown in FIG. 12(e) is caused by a dislocated assembly of lenses, or the like within optical scanning system. Namely, in all of the above cases, the errors are due to mechanical factors.
A printer controller for delivering print data to a color image generator containing a plurality of image forming devices. The printer controller comprises
a receiving buffer region for receiving a certain print data delivered from a source of data input,
a display list region for storing, as a description list covering at least one print page, the print data stored in the receiving buffer region,
a raster data storage region for storing, as raster data, the print data kept in the display list region, and
a corrected raster data storage region for storing the raster data stored in the raster data storage region after being corrected by a skew.multiplying factor corrector, which corrector corrects the skew.multiplying factor that reveal themselves as the relative error at the time when an image is formed. The corrected raster data are delivered to a color image former.
The present invention provides a technology that corrects the dislocation an image by a printer controller in the color image former.